Sputtering is a method of physical vapor deposition (PVD) that involves the removal of material from a solid cathode by bombarding it with positive ions from the discharge of a rare and inert gas such as argon (Ar). The cathode is generally made from a metal or an insulator and, in contrast to thermal evaporation; complex compounds such as high-temperature superconductor (HTS) materials can be sputtered with less chemical composition change. Sputtering is often done in the presence of a reactive gas, such as oxygen and nitrogen, to control or modify the properties of the deposited film.
Although reactive PVD provides a higher deposition rate and generally higher quality films, there are fundamental problems such as non-linear operating parameters and difficulty in providing long-lasting effective electrodes. The specific interrelated problems associated with reactive PVD include: 1) cathode poisoning and anode/ground disappearing, 2) initiation, and 3) shutter control.
The reactive PVD system has two distinguishable stable modes in operation: a poison mode and a non-poison mode. The poison mode occurs when the target becomes fouled by oxide or nitride formation, thus losing its metallic nature. In contrast, the non-poison mode, in addition to normal deposition of dielectric on the substrate, may also be affected by the amount of metal surface left on the target with the result of low dielectric formation.
In order to maintain proper sputtering conditions in the system, it is critical to carefully control the amount of reactive gas in the system, especially in the start-up phase of operation. If an excess of reactive gas is introduced into the system, the target is likely to become fouled and undergo a chemical reaction on its surface, with the result that the desired deposition rate may become low. On the other hand, excess reactive gas at any moment may result in cathode poisoning, anode/cathode disappearing, and/or possible pulling in of the wrong operating mode. In addition, because a dielectric film covers the surface of the target, it is frequently broken by arc discharges. If the system is not supplied with enough reactive gas, then the films produced on the substrate may be low in reactive gas or have reactive gas vacancies. This short supply of reactive gas may result in reactive molecule vacancy in the deposited film. Thus, the control of reactive gas injection is an important factor in achieving desired system performance. In addition, the voltage and current properties are critical, since because they affect the rate of ion formation at the target site.
Therefore, it is desirable to provide a sputtering system with gas flow regulation of a reactive gas to achieve the desired properties of the deposited film. It is also desirable to provide a sputtering system that reduces the need for system cleaning, minimizes poisoning of the system target or anode/ground disappearance, and provides simpler operation than existing coating technologies.